1. Field of the Invention
This invention concerns a display equipment, which performs display at sub-pixel precision based on an original image, which is not a vector image but a raster image (pixel precision: in the case of a font, means not a vector font but a raster font), and art related to this display equipment.
2. Description of the Related Art
Display equipment that employs various types of display devices is in common use. Such display devices include color LCD's, color plasma displays, and other display devices, in which three light-emitting elements, which respectively emit light of the three primary colors of R, G, and B, are aligned in a fixed order to form one pixel. A plurality of the pixels thus formed are aligned in a first direction to form one line. A plurality of lines are aligned in a second direction, which is orthogonal to the first direction, to form a display screen of the display device.
There are also many display devices having relatively narrow display screens which make detailed display difficult to achieve. Such narrow display screens may be found in portable telephones, mobile devices, computers, etc. When an attempt is made to display a small character, photograph, or complex picture, etc. on a small display device, part of the image tends to become smeared and unclear.
To solve the above problem, attempts have been made to display in sub-pixel units. A sub-pixel unit is defined as one of the three light-emitting units. Improved picture quality may be achieved by separately driving the three light-emitting elements for R, G, and B of the pixel.
Literature (titled: “Sub-pixel Font Rendering Technology”) concerning sub-pixel display, discloses on the Internet a system which uses one pixel formed by the three light-emitting elements for R, G, and B to improve the clarity of the display on a narrow screen. The present inventors have checked this literature upon downloading it from the site, http://grc.com, or its subordinate.
This art is described with reference to FIGS. 24 to 28. In the following description, the image of the alphabetic character, “A”, is used as an example of the image to be displayed.
FIG. 24 is a schematic view of a single line in which single pixels are formed from three light-emitting elements as described above. The horizontal direction in FIG. 24 (the direction in which the light-emitting elements of the three primary colors of R, G, and B are aligned) is defined as the first direction. The orthogonal, vertical direction is defined as the second direction. The definition of directions is arbitrary, and is for purposes of description, without the intention to limit the present invention. The order of alignment of the light-emitting elements besides R, G, and B is possible, and this prior art and this invention can be applied in the same way described even if the order of alignment is changed.
A plurality of pixels (sets of three light-emitting elements) are aligned in a single row in the first direction to form a single line. A plurality of lines are aligned in the second direction to form the display screen.
With this sub-pixel technology, the original image is, for example, an image such as shown in FIG. 25. In this example, the character, “A”, is displayed over an area having seven pixels in the horizontal direction and seven pixels in the vertical directions. Where each of the R, G, and B light-emitting elements is handled as a single pixel to perform sub-pixel display, a font, which has a definition of three times that of the above-described image in the horizontal direction, is prepared, as shown in FIG. 26, over an area consisting of 21 (=7×3) pixels in the horizontal direction and 7 pixels in the vertical direction.
Then as shown in FIG. 27, a color is determined for each of the pixels in FIG. 25 (i.e., not the pixels of FIG. 26 but the pixels of FIG. 25). However, since color irregularities will occur if display is performed as it is, a filtering process, using factors such as shown in FIG. 28(a), is applied. Factors concerning the luminance are shown in FIG. 28, and the luminance values of the respective pixels are adjusted by multiplying a factor, for example, of 3/9 in the case of the central target pixel, 2/9 in the case of an adjacent pixel, and 1/9 in the case of the pixel next to the adjacent pixel.
When such a filtering process is applied to pixels of the colors shown in FIG. 27, blue is adjusted to light blue, yellow is adjusted to light yellow, red is adjusted to light red, and cyan is adjusted to light cyan as shown in FIG. 28(b).
An image to which such a filtering process has been applied is then allocated to the respective light-emitting elements of FIG. 26 to perform sub-pixel display.
(First Problem)
With this prior art, an image (FIG. 26), which is magnified by three in definition in the first direction with respect to the original image (FIG. 26), must be retained separately and yet statically.
Generally, with fonts or other sets of numerous images, simply increasing the types of fonts requires increasing the system resource. In particular, an art that requires large system resources is difficult to employ in a portable telephone, mobile computer, etc. where there are several limitations in terms of system resource.
Furthermore, since the art is premised on the ability to statically use the three-time magnified image itself, a display, with which the definition has been magnified by three, cannot be performed, for example, for a facial portrait image or other arbitrary image that has been downloaded from a server.
The prior art has the above-described first problem that, although sub-pixel precision display is not impossible, the burden placed on the system resources is large and the range in which sub-pixel display can be performed is limited.
(Second Problem)
Also, with the prior art, there is a difficulty in terms of adjustment of the character intervals. This point is described by way of the example shown in FIG. 16. The drawing illustrates schematically a sub-pixel display by the prior art. In this example, the character string, “This”, is displayed.
The respective characters (that is, the “T”, “h”, “i”, and “s”) are formed of sub-pixels as shown at the left side of FIG. 16 or as previously prepared font arranged in sub-pixels. Four sub-pixel images are thus obtained for the four characters, “T”, “h”, “i”, and “s”, respectively.
With the prior art, the images of the respective characters are aligned and displayed as shown at the right side of FIG. 16.
However with the prior art, the positions of these four images are set in pixel units and cannot be adjusted more finely. Also, although the four images of “T”, “h”, “i”, and “s” are sub-pixel images, the spaces between these images are not sub-pixel images. There is thus the second problem that when viewed as a whole, a character string, such as “This”, is not fixed in pitch and was thus non-uniform.
Also, in the case of a format such as equal spacing (similar to typewriter spacing), which is shown in FIG. 17(a), since the character intervals can only be adjusted at pixel precision, the character intervals tend to be non-uniform.
(Third Problem)
The prior-art display method enables only a binary black-white display (or a gray-scale display of low gradation) and cannot accommodate the case where at least one of the foreground or background is in color.